An ophthalmic lens, such as a contact lens or an intra-ocular lens, provides vision correction by introducing a refractive element into the optical line of sight. A conventional ophthalmic lens may provide a fixed correction of the dioptric power of an eye. For example, an optical design is determined taking into account information gathered from the patient, and the lens is manufactured according to this personalized design, e.g. by cast molding or lathing. The optical qualities of such a conventional lens thus are static once the lens has been formed.
However, many people suffer from presbyopia, which means that they have trouble accommodating of vision, e.g. their eyes have a limited focal range or changing focus between nearby and remote sceneries takes a long time. Presbyopia is common among people above the age of 40-50 and may for example be caused by a decreased elasticity of the intraocular lens used for accommodation of vision. Bifocal or ‘progressive’ spectacles can provide different dioptric corrections that correct the sight for different viewing distances. This is accomplished by dividing the lenses into juxtaposed zones with different dioptric powers, either with a sharp or a gradual transition between these zones. The desired dioptric power is then selected by moving the line of sight so that it crosses the appropriate zone of the spectacle's lens. However, in a contact lens, since it is in direct contact with the eye, it is not easy to move the line of sight and therefore a multifocal contact lens is not easy to implement. For example, a translational dual focal contact lens is known in the art, in which the wearer can shift the lens upward or downward using eye ball movements in order to select a different dioptric zone in the lens. However, the learning curve of such a lens is very steep and its use is not at all obvious, especially for older people. Furthermore, for intra-ocular lens implants, shifting the lens with respect to the line of sight may be infeasible.
In order to overcome the limitations of conventional contact lenses, dual focal contact lenses are known in the art. In such dual focal contact lenses, two dioptric powers are simultaneously active, leading to two superimposed images, one focused nearby and one remotely focused. However, this has the disadvantage of vision artefacts, such as halos, ghost vision and reduced contrast. Furthermore, dual focal or multifocal contact lenses are known in the art having a plurality of substantially concentric lens zones with different, possibly alternating lens powers. Although such lenses may also lead to superimposed images focused on different distances, due to the concentric arrangement of the lens zones, the effective lens powers will to a certain degree depend on the diameter of the pupil, although there is some optical distance between the latter and the lens. In bright circumstances the pupil diameter is small and the central part of the lens will determine its effective power. In dim lighting circumstances, the pupil dilates, and the influence of the outer rings will be relatively higher. However, the disadvantage of this approach is that there is no guaranteed relationship between pupil diameter and desired lens power. Furthermore, such lens may also be susceptible to vision artefacts such as halos, ghost vision and reduced contrast.
Another approach known in the art involves a lens with an aspheric front or back surface which provides a smooth transition between different focal points from the middle of the lens towards the edge. In such a design the lens operation is also pupil size dependent to a certain degree. Again, such lenses have the disadvantage of being prone to halos, ghost vision and reduced contrast.
Active lenses are also known in the art. For example, U.S. Pat. No. 8,348,424 discloses an ophthalmic lens with a variable optic portion, which is capable of changing the optical quality of the lens, e.g. a cast molded silicone hydrogel contact lens with an energized variable optic insert. Such variable optic insert can for example comprise a liquid meniscus lens with an electrically conducting fluid and oil capable of changing an optical characteristic of the ophthalmic lens.
Furthermore, U.S. Pat. No. 8,348,422 also discloses an energized ophthalmic lens. Embodiments according to U.S. Pat. No. 8,348,422 may comprise activating components within an ophthalmic lens system in response to an external signal, e.g. an eyelid blink or a pressure signal applied to the lens via the closed eyelid.